The invention relates to a plasma display provided with a carrier plate, a transparent front plate, a ribbed structure which subdivides the space between the carrier plate and the front plate into plasma cells, which cells are filled with a gas, with one or several electrode arrays for generating corona discharges in the plasma cells, and with a phosphor layer which comprises a blue-emitting phosphor from the group of doped, europium-activated barium-magnesium aluminates.
The basic principle of a plasma display is that a high voltage generates electromagnetic radiation in a gas of low gas pressure, which radiation may itself be visible or may be converted into visible light by phosphors.
In a color plasma display of conventional construction, the gas filling consists of a rare gas, for example xenon or a rare gas mixture, for example a mixture of helium, neon, and xenon. Ultraviolet radiation in the VUV range is generated in the discharge, i.e. with a wavelength below 200 nm. This VUV radiation excites the red-, green-, and blue-emitting phosphors (RGB phosphors) in the phosphor layer such that they radiate visible light in the colors red, green, and blue. The luminescent materials in plasma displays accordingly utilize the high-energy side of the UV spectrum, unlike conventional fluorescent lamps. The VUV emission may vary between a single line at 147 nm and a wide band around 172 nm, depending on the composition of the rare gas mixture and the gas pressure. This results in new requirements being imposed on the RGB phosphors in a plasma display.
The RGB phosphors are the final link in the energy transfer chain in which electrical energy is converted into visible light in the plasma display. The efficacy of a plasma display with a phosphor layer depends crucially on the electro-optical efficacy of the phosphors, i.e. to what extent the generated UV radiation is absorbed in the phosphor and to what extent subsequently the generated visible light leaves the plasma display in the direction of a viewer.
Among the blue-emitting phosphors, europium(II)-activated barium-magnesium aluminate is unsurpassed as regards its color properties and its electro-optical efficacy. A problem, however, is its comparatively strong degradation under the influence of VUV radiation. The degradation is particularly strong under the influence of VUV radiation with a wavelength below 200 nm and manifests itself in a deterioration of the electro-optical efficacy and in a shift of the color point into the green region.
WO 99/34389 discloses a plasma display with a phosphor having the general formula Ba1xe2x88x92eEueMnmMg1+xcex4xe2x88x92mAl10+2fO17+xcex4+3f, for which the color shift is smaller throughout the life of the display.
The degradation and color shift of the europium(II)-activated barium-magnesium aluminate, however, starts as early as in the manufacture of the plasma display, during which the phosphor layer is exposed to temperatures of 500xc2x0 C. and more.
It is an object of the present invention to provide a plasma display provided with a carrier plate, a transparent front plate, a ribbed structure which subdivides the space between the carrier plate and the front plate into plasma cells, which cells are filled with a gas, with one or several electrode arrays for generating corona discharges in the plasma cells, and with a phosphor layer which comprises a blue-emitting phosphor from the group of doped, europium-activated barium-magnesium aluminates, which has an improved, natural color rendering and a higher brightness.
According to the invention, this object is achieved by means of a plasma display with a carrier plate, a transparent front plate, a ribbed structure which subdivides the space between the carrier plate and the front plate into plasma cells, which are filled with a gas, with one or several electrode arrays for generating corona discharges in the plasma cells, and with a phosphor layer which comprises a phosphor chosen from the group of doped europium(II)-activated barium-magnesium aluminates with the general formula
Ba1xe2x88x92xMxMgAl10O17xe2x88x920.5x:Eu with 0 less than xxe2x89xa60.5 and M=Li, Na, K, Rb and Cs; 
BaMg1xe2x88x92yMyAl10O17xe2x88x920.5y:EU with 0 less than yxe2x89xa60.5 and M=Li, Na, K, Rb and Cs; and 
BaMgAl10xe2x88x92zNzO17xe2x88x920.5z:Eu with 0 less than zxe2x89xa65.0 and N=Mg, Ca, Sr, Ba and Zn 
The blue point has been shifted for a better color saturation in such a plasma display. This influences not only the blue tints, but also all intermediate tints on the lines from blue to green and from blue to red, which become achievable through the enlargement of the color rendering triangle in the blue region. Many color nuances can thus be represented more naturally, which difference is visible. In addition, the color contrast is enhanced at a high ambient brightness.
It is preferred for the present invention that the blue-emitting phosphor comprises 1 to 30 mole % europium(II).
The invention also relates to a phosphor chosen from the group of doped europium(II)-activated barium-magnesium aluminates with the general formula
Ba1xe2x88x92xMxMgAl10O17xe2x88x920.5x:Eu with 0 less than xxe2x89xa60.5 and M=Li, Na, K, Rb and Cs; 
BaMg1xe2x88x92yMyAl10O17xe2x88x920.5y:Eu with 0 less than yxe2x89xa60.5 and M=Li, Na, K, Rb and Cs; and 
BaMgAl10xe2x88x92zO17xe2x88x920.5z:Eu with 0 less than zxe2x89xa65.0 and N=Mg, Ca, Sr, Ba and Zn 
This phosphor is characterized by an improved thermal resistance, in particular in an atmosphere containing oxygen, because the oxidation of the Eu(II) to Eu(III) becomes less. The luminance of this phosphor accordingly does not deteriorate during the manufacture of the plasma display, and the efficacy remains constant for a long time, also under excitation by VUV radiation.